How do I add random spotting to the same face in cycles?
If I understand correctly you try to find a procedural way to make some black and white spots on yout object. Here is a way to do it:


Make the following node chain : Texture Coordinate (Object output) > Voronoi Texture > ColorRamp > Diffuse BSDF > Material Output. With the Voronoi you will create the spots shapes and sizes and with the ColorRamp you will determine the space between the spots.
But as you can see the spots are a little bit too regular. If you want to introduce more accidents, before the Voronoi you can add a Color node > MixRGB (Add mode) and plug a Noise Texture on its other socket. This solution was inspired by Gleb Alexandrov's video.